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Biology IB HL - 5.2 Natural Selection Part 1
This deck covers key concepts of natural selection and genetic variation as proposed by Charles Darwin and others. It includes mechanisms of variation, types of mutations, and the process of meiosis.
Who proposed the theory of natural selection?
The theory of natural selection was posited by Charles Darwin (and also Alfred Wallace) who described it as ‘survival of the fittest’
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Key Terms
Term
Definition
Who proposed the theory of natural selection?
The theory of natural selection was posited by Charles Darwin (and also Alfred Wallace) who described it as ‘survival of the fittest’
What species is most likely to survive, in terms of natural selection?
According to this theory, it is not necessarily the strongest or most intelligent that survives, but the ones most responsive to change
In response to what conditions does natural selection occur (5)?
inherited variation; competition; selection; adaptations; evolution
How does natural selection occur in relation to inherited variation?
Inherited Variation – There is genetic variation within a population which can be inherited
How does natural selection occur in relation to competition?
Competition – There is a struggle for survival (species tend to produce more offspring than the environment can support)
How does natural selection occur in relation to selection?
Selection – Environmental pressures lead to differential reproduction within a population
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| Term | Definition |
|---|---|
Who proposed the theory of natural selection? | The theory of natural selection was posited by Charles Darwin (and also Alfred Wallace) who described it as ‘survival of the fittest’ |
What species is most likely to survive, in terms of natural selection? | According to this theory, it is not necessarily the strongest or most intelligent that survives, but the ones most responsive to change |
In response to what conditions does natural selection occur (5)? | inherited variation; competition; selection; adaptations; evolution |
How does natural selection occur in relation to inherited variation? | Inherited Variation – There is genetic variation within a population which can be inherited |
How does natural selection occur in relation to competition? | Competition – There is a struggle for survival (species tend to produce more offspring than the environment can support) |
How does natural selection occur in relation to selection? | Selection – Environmental pressures lead to differential reproduction within a population |
How does natural selection occur in relation to adaptations? | Adaptations – Individuals with beneficial traits will be more likely to survive and pass these traits on to their offspring |
How does natural selection occur in relation to evolution? | Evolution – Over time, there is a change in allele frequency within the population gene pool |
What is the summary of natural selection (mnemonic) | Inherited variation exists within the population; Competition results from an overproduction of offspring; Environmental pressures lead to differential reproduction; Adaptations which benefit survival are selected for Genotype frequency changes across generations; Evolution occurs within the population; Mnemonic: ICE AGE |
What does natural selection require? | Natural selection requires variation among members of a species in order to differentiate survival (variation needed for selection) |
In what forms can variation arise? | This variation can manifest as either discontinous (distinct classes) or continuous (range across a characteristic spectrum) |
What are the 3 main mechanisms in which variation may occur in an individual? | mutations; meiosis; sexual reproduction |
How do mutations lead to variation? | Mutations – Changing the genetic composition of gametes (germline mutation) leads to changed characteristics in offspring |
How does meiosis lead to variation? | Meiosis – Via either crossing over (prophase I) or independent assortment (metaphase I) |
How does sexual reproduction lead to variation? | Sexual reproduction – The combination of genetic material from two distinct sources creates new gene combinations in offspring |
What is a gene mutation? | A gene mutation is a change in the nucleotide sequence of a section of DNA coding for a specific trait |
What is formed by mutations? | New alleles are formed by mutation |
What 3 types of gene mutations are there? | Gene mutations can be beneficial, detrimental or neutral |
What are beneficial mutations? | Beneficial mutations change the gene sequence (missense mutations) to create new variations of a trait |
What are detrimental mutations? | Detrimental mutations truncate the gene sequence (nonsense mutations) to abrogate the normal function of a trait |
What are neutral mutations? | Neutral mutations have no effect on the functioning of the specific feature (silent mutations) |
What does crossing over involve? (meiosis) | Crossing over involves the exchange of segments of DNA between homologous chromosomes during prophase I |
Where does the exchange of genetic material occur in meiosis? | The exchange of genetic material occurs between non-sister chromatids at points called chiasmata |
What does crossing over lead to in terms of the 4 chromatids? meiosis | As a consequence of this recombination, all four chromatids that comprise the bivalent will be genetically different |
What will the chromatids consist of in meiosis? | Chromatids that consist of a combination of DNA derived from both homologous chromosomes are called recombinants |